Vacuum pump

ABSTRACT

A vacuum pump exhausting gas by rotating a rotor relative to a stator includes a rotor having a ferromagnetic body provided on a rotational axis on, or near, a rotational axis of the end face of a rotational axis direction of a rotational body. The ferromagnetic body&#39;s Curie temperature is approximately equal to an allowable temperature of the rotor. A detecting portion disposed opposite the ferromagnetic body is configured to detect a change in magnetic permeability of the ferromagnetic body based upon a change in inductance. A revolution sensor target and an inductance-type revolution sensor are disposed in such a way as to detect both a revolution of the rotor and a change in the magnetic permeability of the ferromagnetic body. A control device halts rotor rotation when a change in magnetic permeability of the ferromagnetic body is detected and/or when a predetermined integrated time is exceeded.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to vacuum pumps, and more specifically,relates to vacuum pumps that use the change in the magnetic permeabilityof a ferromagnetic body to determine a rotor temperature and/or controlrotor rotation.

In a turbo-molecular pump used for example in semiconductormanufacturing equipment, as the flow rate or molecular weight of the gasexhausted by the turbo-molecular pump increases, the rotor temperatureincreases due to heat generated in association with an increase in motorelectricity or frictional heat associated with gas exhaust. Also, evenin a case wherein the gas with little thermal conductivity is exhausted,the rotor temperature increases. Generally, the higher the number ofrotor revolutions, flow rate, pressure, temperature of exhaust gas, andpump ambient temperature, the higher the rotor temperature.

Since the rotor of a turbo-molecular pump rapidly rotates, centrifugalforce results in large tension stress. Therefore, an aluminum alloyhaving an excellent specific strength is generally used as the rotormaterial. However, an allowable temperature of creep deformation for analuminum alloy is relatively low (approximately 110° C.˜120° C.).Therefore, an operating pump must be constantly monitored to verify thatthe rotor temperature stays below the allowable temperature.

A contactless method for detecting rotor temperature is known and usesthe fact that the magnetic permeability of the ferromagnetic bodygreatly changes at the Curie temperature.

For example, Japanese Patent Publication No. H7-5051 discloses a devicein which a ring-shaped ferromagnetic body is disposed around a rotor.The changes in magnetic permeability of the ferromagnetic body isdetected by a coil as the temperature reaches the Curie temperature.

However, because the ring-shaped ferromagnetic body is installed aroundthe rotor, a high degree of tension stress, due to a centrifugal force,acts on the ferromagnetic body, and may possibly damage theferromagnetic body.

The present invention has been made to solve the above conventionalproblems.

SUMMARY OF INVENTION

A first aspect of the invention includes a vacuum pump exhausting gas byrotating a rotor relative to a stator and includes a ferromagnetic bodyprovided on a rotational axis or near the rotational axis of an end faceof the rotational axis direction of a rotational body that includes arotor whose Curie temperature is approximately equal to an allowabletemperature of the rotor. A detecting portion is provided in such a wayas to oppose the ferromagnetic body and detects changes in magneticpermeability of the ferromagnetic body as the inductance changes.

A second aspect applies to a vacuum pump exhausting the gas by rotatingthe rotor relative to the stator and includes a revolution sensor targetprovided near the rotational axis of the end face of the rotational axisdirection of the rotational body, the rotational body including a rotor.A ferromagnetic body is provided in a position wherein a radialdirectional distance from the rotational axis of the rotor isapproximately equal to the radial directional distance of the revolutionsensor target. The Curie temperature of the rotor is approximately equalto the allowable temperature of the rotor and an inductance-typerevolution sensor is disposed in such a way as to be opposed to therevolution sensor target and the ferromagnetic body. The revolutionsensor detects the number of revolutions of the rotor and the change inthe magnetic permeability of the ferromagnetic body, as the inductancechanges.

A third aspect includes the vacuum pump as disclosed in the firstaspect, wherein the ferromagnetic body is provided on the end face ofthe rotor in such a way that the inductance, when the detecting portionand the ferromagnetic body are opposed to each other, becomes smallerthan the inductance when the detecting portion and the end face of therotor are opposed to each other, when the temperature of the rotor islower than the Curie temperature.

A fourth aspect includes the vacuum pump of the first aspect and furtherincludes a control means that reduces the rotational speed of the rotor,or halts the rotation of the rotor, when the change of the magneticpermeability of the ferromagnetic body is detected.

A fifth aspect includes the control means halting the rotation of therotor when an integration of time wherein the change of the magneticpermeability of the ferromagnetic body is detected, exceeds apredetermined allowable time based on the creep life design of therotor.

A sixth aspect includes an alarm means for presenting alarm informationthat indicates an abnormality of the pump when a change of the magneticpermeability of the ferromagnetic body is detected.

A seventh aspect includes a detecting portion provided in such a way asto be opposed to the first and second ferromagnetic bodies, wherein theCurie temperature of the second ferromagnetic is high than the Curietemperature of the first ferromagnetic. The detecting portion detectsthe change in magnetic permeability of the first and secondferromagnetic bodies as inductance changes. In addition, a control meansis included that halts the rotation of the rotor when a change inmagnetic permeability of the second ferromagnetic body is detected,and/or when the integration time of when the change of the magneticpermeability of the first ferromagnetic body is detected exceeds apredetermined allowable time based on the creep life design of therotor.

Because the ferromagnetic body is provided on or near the rotationalaxis of the end face of the rotational axis direction of the rotationalbody, a tension stress acting on the ferromagnetic body can becontrolled and durability of the ferromagnetic body can be improved.Moreover, because the revolution sensor detects the change of themagnetic permeability of the ferromagnetic body as the inductancechanges, an increase in the number of parts and an increase in cost maybe prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of one embodiment of a vacuum pump according to thepresent invention;

FIGS. 2A and 2B are drawings showing portions of a nut, wherein FIG. 2Ais a cross sectional view and FIG. 2B shows the bottom face of the nut;

FIG. 3 is a drawing depicting inductance changes of a gap sensor;

FIG. 4 is a drawing showing a relationship between a Curie temperatureTc and magnetic permeability;

FIG. 5 is a block diagram of a detecting portion;

FIGS. 6A-6C show signal waveforms based upon the block diagram of FIG.5;

FIG. 7 is a modified first example of the vacuum pump;

FIG. 8 is a cross sectional view of the pump, wherein a target isprovided on the upper end face of a rotor;

FIGS. 9A and 9B illustrates a second embodiment of the vacuum pump,wherein FIG. 9A is a cross sectional view of the nut and a gap sensor,and FIG. 9B is a view taken along 9B of the nut;

FIG. 10 is a block diagram of a detecting portion according to themodified second example of FIGS. 9A and 9B;

FIGS. 11A-11E illustrates signal waveforms based upon the block diagramof FIG. 10;

FIGS. 12A and 12B illustrate a third embodiment of the vacuum pump,wherein FIG. 12A is a cross sectional view of a nut and gap sensor, andFIG. 12B shows the bottom face of the nut;

FIG. 13 is a block diagram of a detecting portion according to the thirdexample; and

FIGS. 14A-14C show waveforms according to the block diagram of FIG. 13.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a drawing showing an embodiment of a vacuum pump according tothe present invention, and shows a schematic structure of a pump mainbody 1 of a magnet-bearing type turbo-molecular pump and a controller30.

A shaft 3 comprising an attached rotor 2 contactlessly supported byelectric magnets 51, 52, 53 is provided on a base 4. The floatingposition of the shaft 3 is detected by radial displacement sensors 71,72 disposed on the base 4 in addition to an axial displacement sensor73. Electric magnets 51, 52 each comprise a radial magnet bearingfurther comprising five axis-control magnet bearings. The electricmagnet 53 constitutes an axial magnet bearing and displacement sensors71-73.

At a lower end of the shaft 3, a circular disk 41 is provided, and theelectric magnet 53 is provided in such a way as to sandwich the disk 41from above and below. The shaft 3 is floated in an axial direction byoperation of the disk 41 being attracted by the electric magnet 53. Thedisk 41 is fixed to the lower end portion of the shaft 3 by a nut 42.

As shown in FIGS. 2A, 2B, a ring-shaped ferromagnetic body target 43 isprovided on the lower end face of the nut 42. The target 43 is embeddedin the nut 42 by adhesion, or fixed to the nut 42 by heating the nut 42side and carrying out shrinkage fitting. When the nut 42, along withshaft 3, is rapidly rotated, a centrifugal force acts on the target 43in a horizontal direction, as shown in the drawings. However, since thetarget 43 is provided in the end face portion of a rotational body, thetarget 43 may be provided near the axis, so that the effect of thecentrifugal force may be reduced. Moreover, since the side face of thetarget, which is the direction of centrifugal action, is retained by aretaining portion 42 a of the nut 42, tension stress generated in thetarget 43 may be controlled, improving durability of the target 43.

Especially in the case wherein the target 43 is shrunk fit, becausecompressive stress acts on the target 43, the effect of the centrifugalforce can be reduced. Also, the target 43 is provided on the end face ofthe shaft 3, so that the outward form of the target 43 can be reducedregardless of the diameter of the shaft 3, and the target 43 can beprovided near the axis of the shaft 3. Hereby, the effect of thecentrifugal force may be reduced.

On the stator side, an inductance-type gap sensor 44 is provided in sucha way as to be opposed to the target 43 provided in the nut 42. Asdescribed below, the gap sensor 44 detects the change of the magneticpermeability, e.g., an inductance change, of the target 43 when therotor temperature is increased more than an allowable temperature.

In the pump shown in FIG. 1, the target 43 is provided on the end faceof the lower side of the disk 41 provided in the shaft 3. However, asshown in FIG. 8, the upper end face of the rotor 2 may be also providedwith the target 43 on the axis of the rotor. In this case, the target 43may be discoidal and not ring-shaped, and the side face of the target43, upon which the centrifugal force acts, is retained by the rotor 2.More specifically, the rotor 2 functions as the retaining portion of thetarget 43. A gap sensor 44B is retained on the axis of the rotor by asupport 45 fixed to a spacer 10 on the highest level. The gap sensor 44Bhas a structure wherein coils 401 are rolled around in the center of theprojection of a core 400. Because the target 43 in FIG. 8 is provided onthe rotor axis, the target 43 in FIG. 8 may reduce the effect of thecentrifugal force more than the target 43 shown in FIG. 1.

In the rotor 2 in FIG. 1, rotating wings 8 with multiple levels areformed along a direction of a rotational axis. Fixed wings 9 arerespectively provided between the rotating wings 8 lined up above andbelow. Durbin wing levels of the pump main body 1 are formed by therotating wings 8 and fixed wings 9. Each fixed wing 9 is retained byspacers 10 in such a way as to be clamped above and below. The spacers10 maintain gaps between the fixed wings 9 at predetermined intervalsand function to maintain the position of the fixed wings 9.

Moreover, screw stators 11 are provided in back levels (below in thefigure) of the fixed wings 9, and comprise drag pump levels. Gaps areformed between inner circumferential surfaces of the screw stators 11and a cylinder portion 12 of the rotor 2. The fixed wings 9 retained bythe rotor 2 and the spacers 10 are housed inside a casing 13 wherein aninlet 13 a is formed. The shaft 3 is contactlessly supported by electricmagnets 51˜53. When the shaft 3, to which the rotor 2 is attached, isrotated by a motor 6, gas on an inlet 13 a side is exhausted to aback-pressure side (space S1) in the manner of an arrow G1. The gasexhausted to the back-pressure side is exhausted through an auxiliarypump connected to an outlet 26.

The turbo-molecular pump main body 1 is controlled by the controller 30.Controller 30 comprises a magnet-bearing drive control portion 32controlling the magnet bearings; and a motor drive control portion 33controlling the motor 6. A detecting portion 31 detects whether themagnetic permeability of the target 43 is changed or not, based on anoutput signal of the gap sensor 44.

The output signal of the gap sensor 44 is input into the detectingportion 31, and a rotor temperature monitor signal is output into themotor drive control portion 33 and an alarm portion 34. In someembodiments, an output terminal configured to output the rotortemperature monitor signal to the outside of the controller 30 may beprovided. The alarm portion 34 is an alarm means presenting alarminformation, such as an abnormal rotor temperature, etc., to anoperator, and may comprise a display unit displaying a warning messageor may comprise a speaker releasing a warning sound, or a warning and soon.

FIG. 3 illustrates an inductance change of the gap sensor 44, and apattern diagram of a magnetic circuit that may be made by the gap sensor44 and the target 43. The gap sensor 44 is formed by furling a coilaround a core with large magnetic permeability such as a silicon steelplate. A high-frequency voltage with constant frequency and a constantvoltage may be applied to the coil of the gap sensor 44 as a carrierwave, and a high-frequency magnetic field may be formed between the gapsensor 44 and the target 43.

The material that comprises the ferromagnetic body includes a Curietemperature Tc that is approximately the same temperature as theallowable temperature Tmax of the rotor 2, or near the allowabletemperature Tmax of the rotor 2, and comprises the material of thetarget 43. In the case of the rotor 2, the allowable temperature Tmaxwhich generates a creep deformation in the rotor material, is used. Inthe case of aluminum, the allowable temperature Tmax is approximately110° C.˜120° C. Nickel and zinc ferrite, or manganese and zinc ferriteand so on are used for materials of the ferromagnetic body wherein aCurie temperature Tc is approximately 120° C.

FIG. 4 illustrates wherein the magnetic permeability of a target 43rapidly decreases to approximately a vacuum magnetic permeability μ_(o)when the temperature of the target 43 increases to a temperature nearthe Curie temperature Tc. Such an increase may be due, for instance, toan increase of the rotor temperature. When the magnetic permeability ofthe target 43 changes as a result of the magnetic field formed by thegap sensor 44, the inductance of the gap sensor 44 changes. As a result,the carrier wave is amplitude-modulated, and the amplitude-modulatedcarrier wave that is output from the gap sensor 44 is detected andrectified. Therefore, a signal change corresponding to the change of themagnetic permeability can be detected.

The ferromagnetic body, such as ferrite, etc., may be used as the corematerial of the gap sensor 44. However, in the case wherein the magneticpermeability is larger than the magnetic permeability of the air gap, itmay be possible to ignore the magnetic permeability of the air gap.Furthermore, in the case wherein the leakage flux can be ignored, therelationship between inductance L and dimensions d, d₁ are shownapproximately in the following formula (1), wherein N represents thefurled number of the coil, S represents a cross-sectional area of thecore opposed to the target 43, d represents the air gap, d₁ representsthe thickness of the target 43, μ₁ represents the magnetic permeabilityof the target 43, and the magnetic permeability of the air gap isequivalent to the vacuum magnetic permeability μ_(o).

L=N ² /{d ₁/(μ₁ ·S)+d/(μ_(o) ·S)}  (1)

When the rotor temperature is lower than the Curie temperature Tc, themagnetic permeability of the target 43 is sufficiently large compared tothe vacuum magnetic permeability μ_(o). As a result, d₁/(μ₁·S) decreasesto the degree of being able to be ignored compared to d/(μ_(o)·S), sothat formula (1) can approximate to the following formula (2):

L=N ² ·μ _(o) ·S/d   (2)

On the other hand, when the rotor temperature rises more than the Curietemperature Tc, approximately μ₁=μ_(o).

Therefore, in this case, formula (1) is represented in the followingformula (3):

L=N ² ·μ _(o) ·S/(d+d ₁)   (3)

More specifically, the air gap has changed from d to (d +d_(i)), and theinductance of the gap sensor 44 changes accordingly. Whether or not therotor temperature exceeds the Curie temperature Tc may be monitored bydetecting the inductance change at the detecting portion 31 of thecontroller 30.

FIG. 5 is a block diagram of the detecting portion 31, and FIGS. 6A-6Eillustrate signal waveforms A-E generated based upon the block diagramof FIG. 5. When the carrier wave as shown in FIG. 6A is applied to thegap sensor 44 by a power source 60, gap sensor 44 outputs modulationwaves, as shown in FIG. 6B. When the rotor temperature T exceeds theCurie temperature Tc at time tc, the magnetic permeability μ₁ of thetarget 43 decreases such that μ₁ approximately equals μ_(o).Accordingly, the inductance L decreases from a value shown in theformula (2) to a value shown in the formula (3), decreasing theamplitude of the carrier wave.

By inputting the signal in FIG. 6B into a detection circuit 61, a signalshown in FIG. 6C may be obtained. Moreover, by processing the signal inFIG. 6C, e.g., by a rectification circuit 62, a smooth signal as shownin FIG. 6D may be obtained that may serve as an input into a comparator63. The comparator 63 compares an input signal with the threshold Vo,and when the level of the input signal exceeds the threshold Vo, thecomparator 63 outputs a signal of v=H. When the level of the inputsignal is decreased to be less than the threshold Vo, the comparator 63outputs a signal of v=L (refer to FIG. 6E). A signal output from thecomparator 63 is output to the motor drive control portion 33 and thealarm portion 34 as the rotor temperature monitor signal.

Pump Operation

A method for safely operating a turbo-molecular pump by using a rotortemperature monitor signal t output from a detecting portion 31, isdisclosed below.

OPERATION EXAMPLE 1

The operation example 1 is the easiest operation. When the rotortemperature monitor signal v becomes v=L, the motor drive controlportion 33 immediately reduces the speed of the rotation of a rotor 2,stopping the rotor 2. An alarm portion 34 informs abnormality of therotor temperature. When the rotor temperature T becomes the allowabletemperature Tmax and there are significant creep deformations, thegeneration of the above-mentioned creep deformations may be prevented bystopping the rotation of the rotor, improving the safety of the pump.

OPERATION EXAMPLE 2

In the operation example 1, the rotor temperature monitor signal is v=Land the rotation of the rotor is stopped. However, the revolution ofrotor 2 may be decreased only during the signal of v=L, and may bereturned to the rated speed again at a time wherein the rotortemperature monitor signal becomes v=H. When the rotor temperature Texceeds the Curie temperature Tc, creep deformation of the rotor 2 dueto the centrifugal force may be controlled by decreasing the number ofrevolutions. In addition, when the number of revolutions is decreased tobe less than the rated speed, not only is the increased rotortemperature information displayed, but the operator may be alerted bydisplaying the number of decreased revolutions in the alarm portion 34.

Also, when the turbo-molecular pump is used to etch equipment and so on,a reaction product may be easily attached to the inside of the pump. Asthe temperature of the pump decreases, the pump main body may be heatedby a heater and the like, helping to prevent reaction product from beingattached. Consequently, instead of a decrease of the rotor revolution,or with a decrease of the rotor revolution, a heating means such as aheater and the like, may be halted only during the signal of v=L.

OPERATION EXAMPLE 3

In the operation examples 1, 2, when the rotor temperature monitorsignal becomes v=L, the rotation of the rotor may be stopped, or therotor revolution may only be decreased when the signal of v=L. However,there is a case wherein the rotation of the rotor cannot be changed dueto being in the middle of the process on a semiconductor equipment side.As an example, when an integrated value of the time when the signal isv=L becomes the predetermined criterion time, the rotor 2 is halted andthe generation of the abnormality is informed by the alarm portion 34.

Therefore, even when temperature T become wherein T≧Tc during theprocess, if the integrated time is within the criterion time, theprocess can be continued without change.

The criterion time is the time to reach allowable deformation volume ofthe rotor 2 and is obtained beforehand by the creep life design of therotor. However, since the creep deformation differs depending, forexample, on the temperature, the criterion time may be calculated basedupon the condition that the rotor temperature T is the Curie temperatureTc, or may be a shorter time than the previously-described time.

MODIFIED EXAMPLE 1

FIG. 7 is a cross sectional view of a nut 42 comprising theturbo-molecular pump. Other than nut 42, the structure of the pump mainbody 1 of FIG. 7 is the same as the structure shown in FIG. 1. In themodified example 1, in addition to the target 43, a target 43B with ahigh Curie temperature is added to the nut 42, as a target of the gapsensor 44. In this case, formula (4) shown below may be approximatelyreplaced by the above-described formula (1). The thickness of the target43B may be d₂, the magnetic permeability is μ₂, and the Curietemperature is Tc′, wherein Tc′>Tc.

L=N ² /{d ₁/(μ₁ ·S)+d ₂/(μ₂ ·S)+d/(μ₀ ·S)}  (4)

When the rotor temperature T exceeds the Curie temperature Tc,approximately μ₁=μ₂=μ₀, so that the inductance L of the gap sensor 44changes as follows depending on the rotor temperature T.

(T<Tc) L=N ²·μ₀ ·S/d

(Tc≦T<Tc′) L=N ²·μ_(o) ·S/(d+d ₁)

(T≧Tc′) L=N ²·μ_(o) S/(d+d ₁ +d ₂)

In the case of the modified example 1, by conducting the followingcontrol action, the pump can be more safely operated. More specifically,the time wherein the inductance is L1 is integrated, and in the casewherein the integrated time is within the criterion time, the operationis continued, and when the integrated time exceeds the criterion time,the rotation of the rotor 2 is halted. However, in the case wherein therotor temperature T exceeds the Curie temperature Tc′ of the target 43B,even if the integrated time is within the criterion time, the rotationof the rotor 2 is halted. This is because the creep deformation alsobecomes significant, such as when the rotor temperature T becomes theCurie temperature Tc′, which is furthermore higher than the allowabletemperature Tmax. Accordingly, the rotor 2 is immediately halted forsafety. Motor drive control portion 33 is configured to calculate theintegrated time.

MODIFIED EXAMPLE 2

FIGS. 9A and 9B illustrate a modified example 2 of the turbo-molecularpump. FIG. 9A is a cross sectional view of the nut 42 and a gap sensor44B. FIG. 9B is a view taken along B of the nut 42. The structure of thepump main body 1, other than the nut 42 and the gap sensor 44B, is thesame as the structure shown in FIG. 1, and the structure of the gapsensor 44B is the same as the structure shown in FIG. 8.

On the bottom face of the nut 42, a target 43C for monitoring the rotortemperature and a depression 42 b, which is a revolution sensor targetfor monitoring the rotor rotation, are provided relative to one gapsensor 44B. The discoid target 43C has a thickness d₁, and a circulardepression 42 b, with a depth d₃, is provided in a position ofrotational symmetry through 180 degrees relative to the central axis ofthe nut 42, and when the nut 42 rotates. The target 43C and thedepression 42 b are alternately opposed relative to the gap sensor 44B.More specifically, in the modified example 2, the gap sensor 44Bfunctions as a revolution sensor and as a sensor that monitors the rotortemperature. D₁ and d₃ are set such that d₃>d₁. Although the target 43Cis described as a disk and the depression 42 b is disclosed as a circle,the target 43C and the depression 42 b are not limited to theabove-mentioned shapes.

FIG. 10 is a block diagram of the detecting portion 31 according to FIG.1, and FIG. 11 illustrates the signal waveforms a-e, referenced in theblock diagram of FIG. 10. In FIG. 11, the reference tc represents a timewherein the temperature of the target 43C exceeds the Curie temperatureTc. Before time tc (shown in the left side of the figures) the rotortemperature T is defined wherein T<Tc. After time tc (shown in the rightside of the figures), the rotor temperature T is wherein T≧Tc.

A carrier wave signal as shown as FIG. 6A, is applied to the gap sensor44B, as signal (b) of FIG. 5. The carrier wave is modulated by the gapsensor 44B, and modulation waves shown as in FIG. 11 are output from thegap sensor 44B. The inductance L of the gap sensor 44B differs dependingon which part of the nut 42 is opposed to the gap sensor 44B. When therotor temperature T fulfils the equation wherein T<Tc relative to theCurie temperature Tc of the target 43C, the inductance L changes as thefollowing formula.

(Opposed to Bottom Face of Nut 42) L=N ²μ_(o) ·S/d

(Opposed to Depression 42b) L1=N ²·μ_(o) ·S/(d+d ₃)

(Opposed to Target 43C) L=N ²·μ_(o) ·S/d

On the other hand, when the rotor temperature T is where T>Tc, theinductance L changes as the following formula, wherein the relativesizes of the inductances L, L1, L2 are L>L2>L1. In other words, sizes d₁and d₃ are set in order to meet the condition of L>L2>L1.

(Opposed to Bottom Face of Nut 42) L=N ²·μ_(o) ·S/d

(Opposed to Depression 42b) L1=N ²·μ_(o) ·S/(d+d ₃)

(Opposed to Target 43C) L2=N ²·_(o) ·S/(d+d ₁)

Therefore, in signal of FIG. 11A, on the left side of the time tc,portions of signal levels D1 and signal levels D2 corresponding to theinductances L, L1 appear on the modulation waves. On the other hand, inthe field of the right side of the time tc wherein the time tc becomesT≧Tc, portions of signal levels D3 corresponding to the inductance L2appear on the modulation waves in addition to the signal levels D1, D2.The signal levels D2 are generated each time the nut 42 makes onerevolution, and an interval between each signal level D2 and each signallevel D3 corresponds to a one-half revolution.

If the modulation waves (a) shown in FIG. 11A are passed through thedetection circuit 61 shown in FIG. 10, signals as shown in FIG. 11B canbe obtained. Moreover, by processing signal of FIG. 11B at therectification circuit 62, signal of FIG. 11C can be obtained. The signal(c) of FIG. 10 is output from the rectification circuit 62 and isdivided into two sections. The signals serve as respective inputs to acomparator 64 for detecting a rotational signal and a window comparator65 for detecting a temperature monitor signal.

The comparator 64 compares input signal of FIG. 11C with the thresholdV₁, and when the signal level is below the threshold V₁, a signal ofFIG. 11D, having a signal level H, is output. When the signal level islarger than the threshold V₁, a signal L is output. In this case, thesignal H is output only at the time of the signal level D2, and in othercases, the signal L is output. Accordingly, pulse signals of FIG. 11Dare output at the motor drive control portion 33 in FIG. 1 from thecomparator 64, as a revolution signal.

Pulses as shown in signal of FIG. 11D are output when the signal levelis D2, i.e., when the gap sensor 44B is opposed to the target 43C.Accordingly, each time the rotor 2 rotates once, pulses are output.These pulses are constantly output, regardless that the rotortemperature T is higher or lower than the Curie temperature Tc. In themotor drive control portion 33, the rotor revolution can be obtained bycounting these pulses.

The window comparator 65 that detects the temperature monitor signalcompares the input signal (c) with the threshold Vmax and Vmin. When thesignal level is over Vmin and below Vmax, a signal level H is output,and when the signal level is smaller than the threshold Vmin or greaterthan the threshold Vmax, the signal L is output (see signal of FIG. 11E). Therefore, pulse signals as shown in FIG. 11F are output at the motordrive control portion 33 and the alarm portion 34 from the windowcomparator 65, as the rotor temperature monitor signal.

As signal of FIG. 11C shows, the signals of level D3 are output onlywhen the rotor temperature T exceeds the Curie temperature Tc.Accordingly a pulse is generated only at the time of T≧Tc, regardless ofwhether or not the rotor temperature T, where T≧Tc can be determined bydetecting the pulse.

Conventionally, there was no device able to be used for both the gapsensor and the revolution sensor of the ferromagnetic body for detectingthe temperature; however, in the above-mentioned modified example 2, gapsensor 44B is provided as a revolution sensor and is used for detectingthe rotor temperature. As a result, costs based on additional componentscan be controlled. Furthermore, there is no need for providing a newspace for a sensor for detecting the rotor temperature.

MODIFIED EXAMPLE 3

FIGS. 12A, 12B refer to a modified example 3 of the turbo-molecularpump. FIG. 12A is a cross sectional view of the nut 42 and the gapsensor 44B and FIG. 12B is bottom face of the nut 42. The structure ofthe pump main body 1, other than the nut 42 and the gap sensor 44B, isthe same as that shown in FIG. 1. Of target 43C, only an exposed surfacehaving a size d4 is depressed, rather than the bottom face of the nut42. As a result, in the case of T<Tc, when the nut 42 rotates, theinductance L changes according to the position of the gap sensor 44B asthe following formula.

(Opposed to Bottom Face of Nut 42) L=N ² ·μo·S/d

(Opposed to Target 43c) L3=N ² ·μo·S/(d+d ₄)

On the other hand, in the case wherein the rotor temperature T is T≧Tc,the inductance L changes as the following formula. At this time, sizesof the inductances L, L3, L4 are L>L3>L4.

(Opposed to Bottom Face of Nut 42) L=N ² ·μo·S/d

(Opposed to Target 43C) L4=N ² ·μo·S/(d+d ₁ +d ₄)

FIG. 13 shows a block diagram of the detecting portion 31. The windowcomparator 65 in the block diagram shown in FIG. 10 is replaced with acomparator 66. FIG. 14 show signal waveforms (a)-(c) referenced in FIG.13. In signal (a) of FIG. 14, a level D4 is output when the inductanceis L3, and signals of levels D5 are output when the inductance is L4.

The comparator 64 compares an input signal with the threshold V₁, andwhen the level of the signal exceeds the threshold V₁, the comparator 64outputs a signal of level H, and when the level of the input signal isdecreased less than the threshold V₁, the comparator 64 outputs a signalL. Since both signal levels D4, D5 are smaller than the threshold V₁,pulse signals corresponding to the signal levels D4, D5 are generated inthe revolution signal which is output from the comparator 64, as shownin FIG. 14B. These pulses are generated every time when the rotor 2makes one rotation.

On the other hand, the comparator 66 that detects the temperaturemonitor signal compares the input signal with the threshold V₂ which islower than the threshold V₁, and when the signal levels exceed thethreshold V₂, the signal level H is output, and when the signal levelsare smaller than the threshold V₂, the signal level L is output. In thiscase, as shown in signal (c) of FIG. 14, the signals of level D5 areoutput only when the rotor temperature T exceeds the Curie temperatureTc. As a result, a pulse is also generated only at the time of T≧Tc.More specifically, whether or not the rotor temperature T is T≧Tc can bedetermined by detecting the pulse.

Even in the modified example 3, since the gap sensor 44B is used as therevolution sensor and also the rotor temperature monitor sensor, themodified example 3 can have the same effects of the modified example 2.

In the above-mentioned modified example 1, the ring-shaped targets 43,43B are overlapped in an axial direction. However as shown in therelationship between the target 43C and the depression 42 b shown inFIGS. 9A, 9B, the targets 43, 43B may be arranged separately in anaxisymmetric position.

The technique shown in the modified example 1 wherein two kinds offerromagnetic bodies, whose Curie temperatures differ are the targetsfor a temperature monitor, or in the modified examples 2 and 3, whereinthe gap sensor is also used for a sensor detecting the change of themagnetic permeability of a temperature monitor target and revolution, isnot limited to the vacuum pump wherein the target for the temperaturemonitor is provided in the end face as described in the above. Aconventional ferromagnetic body ring can be also applied to a devicewith a type of being provided around the rotor. Furthermore, providedthat the above disclosed features are provided, the present invention isnot limited to the above-mentioned embodiment.

Non-limiting, the motor drive control portion 33 comprises a controlmeans for controlling the operation of the motor; the target 43 in FIG.7 comprises the first ferromagnetic body; and the target 43B comprisesthe second ferromagnetic body, respectively.

The disclosure of Japanese Patent Application No. 2004-271680 filed onSep. 17, 2004 is incorporated by reference in its entirety.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. A vacuum pump configured to exhaust gas by rotating a rotor relativeto a stator, comprising: a ferromagnetic body provided on or near arotational axis of an end face of a rotational axis direction of arotational body including said rotor, the ferromagnetic body having aCurie temperature approximately equal to an allowable temperature ofsaid rotor; and a detecting portion provided in such a way as to beopposed to the ferromagnetic body and configured to detect a change inmagnetic permeability of the ferromagnetic body based upon a change ininductance.
 2. A vacuum pump configured to exhaust gas by rotating arotor relative to a stator, comprising: a revolution sensor targetprovided near a rotational axis of an end face of a rotational axisdirection of a rotational body including said rotor; a ferromagneticbody provided in a position wherein a radial directional distance fromthe rotational axis of said rotor is approximately equal to a radialdirectional distance of said revolution sensor target, and a Curietemperature of the ferromagnetic body is approximately equal to anallowable temperature of said rotor; and an inductance-type revolutionsensor disposed in such a way as to be opposed to said revolution sensortarget and said ferromagnetic body, said revolution sensor beingconfigured to detect a revolution of said rotor and a change in magneticpermeability of said ferromagnetic body as a detected inductance change.3. A vacuum pump according to claim 1, wherein said ferromagnetic bodyis provided on the end face of said rotor in such a way that a detectedinductance when said detecting portion and said ferromagnetic body areopposed to each other, becomes smaller than a detected inductance whensaid detecting portion and the end face of said rotor are opposed toeach other, when the temperature of said rotor is lower than the Curietemperature.
 4. A vacuum pump according to claim 1, further comprisingcontrol means for reducing speed of rotation of said rotor or haltingthe rotation of said rotor when change in the magnetic permeability ofsaid ferromagnetic body is detected.
 5. A vacuum pump according to claim1, further comprising control means for halting rotation of said rotorwhen an integrated time, wherein change of the magnetic permeability ofsaid ferromagnetic body is detected, exceeds a predetermined allowabletime based on a creep life design of said rotor.
 6. A vacuum pumpaccording to claim 4, further comprising alarm means for presentingalarm information regarding abnormality of the vacuum pump when thechange of the magnetic permeability of said ferromagnetic body isdetected.
 7. A vacuum pump configured to exhaust gas by rotating a rotorrelative to a stator, comprising: a first ferromagnetic body provided onor near a rotational axis of an end face of a rotational axis directionof a rotational body including said rotor, the first ferromagnetic bodyhaving a Curie temperature approximately equal to an allowabletemperature of said rotor; a second ferromagnetic body provided on ornear the rotational axis of the end face of the rotational axisdirection of said rotor, the second ferromagnetic body having a Curietemperature higher than the Curie temperature of the first ferromagneticbody; a detecting portion provided in such a way as to be opposed tosaid first and said second ferromagnetic bodies, and configured todetect a change in the magnetic permeability of said first and saidsecond ferromagnetic bodies as an inductance changes respectively; andcontrol means for halting rotation of said rotor when at least one ofthe change in the magnetic permeability of said second ferromagneticbody is detected, and when an integrated time, wherein the change of themagnetic permeability of said first ferromagnetic body is detected,exceeds a predetermined allowable time based on a creep life design ofsaid rotor.